Method of making laminated sheet material



United States METHOD OF MAKING LAMINATED SHEET MATERIAL Jay F. Strawinski, Balt'unore, Md.

No Drawing. Application January 11, 1954 Serial No. 403,459

16 Claims. (Cl. 154-124) This invention relates to paper and methods of making I the same and more particularly to paper having'improved and controllable characteristics not heretofore available.

In my prior Patent No. 2,546,705, I have disclosed a paper suitable for a wide variety of purposes and in which a prestretched polyvinyl alcohol film has provided on the exterior faces thereof layers of thin soft pliable absorbent sheet material. While the article and methods therein disclosed are suitable for many purposes it has been ascertained that certain changes and improvements as hereinafter set forth expedite the production and provide a further improved product.

In my prior patent, also, I referred to the use of commercially available previously plasticized polyvinyl alcohol film. It has been ascertained that the film as obtained from different sources does not always have the same characteristics insofar as its use and end result are concerned. For example in carrying out the processes of my prior Patent No. 2,546,705, it was ascertained that there was a tendency, withpolyvinyl alcohol film from certain sources, and after lamination, for the outer lamina to separate from, the central film upon immersion in water by reason of shrinkage of the film.

In accordance with the present invention improved methods are provided which give a product free from objectionable separation, regardless of minor source variations.

In accordance with the present invention, also, improved methods are provided which permit of an increased stretching of the central web while maintaining the integrity of the web and avoiding pin holeformation therein.

In accordance with the present invention, also, improved methods are provided in which the interior'web,

after lamination, and by appropriate treatment has greater stretchability imparted thereto.

In accordance with the present invention, also, improved methods are provided by which the interior web is given a stabilizing treatment so that the likelihood of pin hole formation in the central web is greatly reduced anda better product is obtained.

In 'accordance with the present invention, also, improved methods are provided which include a stretching of the interior web followed by a relaxing, and which maybe followed by a heat treatment of the 'paper after laminatiomso that a better product is obtained.

Other objects and advantageous features of the invention will be apparent from the specification and claims.

The nature and characteristic features of the invention will be more readily understood from the following description, although it will of course, be understood that various modifications and changes can be made in the structure and methods disclosed without departing from the spirit of the invention.

The 'paper, in accordance with the present invention, preferably is formed of. an interior web or layer, having on each exterior face thereof an exterior web or layer, the exterior webs or layers preferably being of the same 2,867,560 Patented Jan. 6, 1959 such as regenerated cellulose, metal foil, and the like,

or may be fibrous material, such as paper. In the preferred application of the invention for each of the exterior layers there is employed a single web or layer of a thin, soft, absorbent porous paper, creped or not, as desired, which is preferably relatively non-sized, of the type known as facial cleaning tissue or cellulose wadding. The interior layer or web preferably consists of a precast or preformed film or sheet of a hydrophilic colloid, organic or inorganic, which has the characteristic of absorbing water and swelling, but not dissolving or dispersing in cold water or water at room temperature when. in film or sheet form. The film or sheet should also have the ability to maintain its integrity during the stretching operations, hereinafter described, and during the combining with the exterior webs or layers so that it is free from cracks or holes, including minute pin holes, and so that the fibers in one outer layer are kept separated from the fibers in the other outer layer.

For the interior layer or Web I prefer to use, as a material possessing the desired characteristics, polyvinyl alcohol film, preferably such as is commercially available in previously plasticized form, of the type which is relatively insoluble in cold water or water at ordinary room temperature and which is conditioned as hereinafter explained. While there is some variation in the characteristics of the polyvinyl alcohol film from different sources of manufacture, the methods of the present invention have been found to be satisfactory for most purposes.

Polyvinyl alcohol film of the order of 1 mil (0.001") in cross section thickness may be utilized after suitable treatment although a thicker or thinner film could be employed so long as it is suitably treated to obtain, or so that it has, the desired characteristics hereinafter referred to.

In order to condition such a film or sheet of the thickness indicated and to providea very thin, highly pliable and soft finished paper, the film or sheet is subjected to a stretching action of predetermined extent, in a plurality of directions. While the stretching may be efiected in three or more directions, simultaneously or in a selected sequence, it is preferred for simplicity to effect the stretching in two directions in sequence at right angles to each other, but in any event so that the resultant is an increase in dimensions laterally and longitudinally, although not necessarily with the same increase in both dimensions.

The stretching operation is preferably carried out at room temperature, of the order of 65 to F. and in an atmosphere of high humidity. The environment for this purpose is preferably saturated withv moisture at the temperature at which it is carried out.

A preferred practice is to wet the film with water at room temperature on both faces by means of a suitable applicator, such as with doctor blades, in the water saturated atmosphere, and draw the film in one direction to from three to five times its original linear dimension in that direction, and then while still maintained in the saturated atmosphere, and without any further direct application of-water, the film is then given a further stretch, in a'direction at right angles or normal to the direction of the first stretching to from three to five times its original dimension in the latter direction.

While the exact action which occurs is not fully un derstood, it is believed that when the stretching of the film to extremely fine gauges is carried out in a saturated atmosphere there is an absorption or perhaps an adsorption on the film surface of just sufiicient water molecules from the moisture vapor saturated environment to give the proper plasticizing and strengthening effect to the film. This provides a delicate and in a sense automatic application of water so that undermoistening and overmoistening with their attendant objections, are avoided. The application of the moisture to the film during stretching in this manner obviates, also, the necessity for using glycerine or other softeners to aid in effecting the stretching and thus facilitates as well 'as reduces the cost of this part of the operation.

The application of moisture to the film during the stretching, as previously described herein, improvesthe character of the film in preparation for later stages in the operation.

If the polyvinyl alcohol film to be stretched has not been newly cast, and has lost through evaporation some of its original water content, or in some instances with newly cast film, it has been found desirable to. pretreat the film, before stretching, by passing the film through a water vapor saturated atmosphere. at a temperature of the order of 75 to 90 F.

While it is not entirely certain as to the exact character of change which takes place attendant upon the stretching it isbelieved that a molecular orientation occurs, at least in and on the. surface of the film, and that this orientation tends to set upon drying of the film in the stretched condition.

After the film has been brought to the desired condition of stretch, say to an area of the order of ten or more times the original area, an improved character of end product is obtained if the stretched film is permitted to shrink or relax to the extent of about 5 to 10 percent of the fully stretched area. This seems to have the effect of reducing internal tensions in the film and of reducing the tendency to pin hole formation in the film, particularly if subsequent heat treatment is applied to the paper after lamination.

This permitted shrinkage also tends to make a film which is tougher at subsequent stages of treatment or use,

and permits of greater ease of handling the film. This character of treatment has'a stabilizing effect on the film which is further enhanced by subsequent heat treatment as hereinafter explained.

After the film has been given the desired stretch, with or without the relaxing or stabilizing, just described,

and with the film maintained in the desiredstretched condition, with the moisture present or with remoistening if necessary, the exterior webs or layers of the desired character are brought into contact with the moistened faces of the film under a low pressure of the order of. If the exterior webs one to five pounds per square inch. or layers are of thin, soft, .pliable, absorbent sheet material, the layers of this material in moistened, condition are brought into contact with the moistened faces. of. the film and the Whole then dried under a low pressure of the order of one to five pounds per square inch. The interior layer or film, in moistened condition is tacky and the exterior layers are adherent thereto. During the drying, the laminated material is preferably maintained in stretched condition. The application of the exterior webs or layers. to the interior web or layer in this manner provides between the layers a non-penetrating bond, which appears to differ from the usual mechanical bond between and around fibers of the outer layers. This nonpenetrating bond maybe effected as a result of some form of physics-chemical attraction between the components of the bonding material and the fibers of the outer layers.

If desired, and after the exterior layers have been brought into contact with the-moistened faces of thefilm, the laminated material may be permitted to contract in one or more directions and at the desired angles to provide a creped effect Without the necessity for employing any other creping operation.

While the paper thus obtained has an improved character, with polyvinyl alcohol film from certain sources, upon immersion of the finished paper in water, a tendency of the outer layers to separate from the central layer has been noted, this arising because of a tenden y of 6 V v v inner layer or film to shrink upon immersion in cold water v or water at room temperature and subsequent drying, particularly if it has not been subjected to the relaxlng or stabilizing treatment described above. Such shrinkage may be of the order of 25 to 50% of the area of greatest extension.

I have ascertained that the shrinkage upon immersion in cold water or water at room temperature and drying, can be greatly reduced if a further stabilizing treatment is ac" corded the finished paper after lamination. A heat treat ment is accorded the laminated sheets which is of such character that pin hole formation in the inner lamina and charring of the outerlamina are avoided by remaining below determinable limits. The temperature employed must be adjusted to the time of exposure to the heat so as to avoid potential injury to the various laminae. As a specific example, exposure of the paper for from about A to about 1 second between heated metal plates at a temperature of 440 to 460 F. hasbeen foundgtoproduce satisfactory results and ispreferred. Lowertemperatures have been employed, for longer time intervals, and an exposure at temperatures of from. about 3607 toabout 375 F. for from about 75 toabout seconds is satisfactory for some purposes. With infra red lamps, exposures for 2 to 3 seconds at temperaturesin the range of about 625 to 675 F. have been found satisfactory. If radiant heatfrom a single heated metal, surface, with an opposed reflecting. surface such as polished,v steel, aluminum or the like with a porous, heatresistantcloth interposed between the heated surface, and thelaminate, and with a light pressing action, thetime interyal may be from /2 to 1 /2 seconds at a temperature. of from 450 to 500 F. When the heat treatment is employed, it has been found very desirable to permitthe film to shrink at least 5 to 10% of its maximumarea. This shrinkage may be effected either before lamination orafter lammm tion and before the application of the heat, to, prevent pin hole formation in the film.

An important effect of theheat treating, is the reduction of any tendency to spontaneous delamination upon immersion, in cold water or water at roomtemperature attendant upon film from certain sources a-reduction in shrinkage upon drying to aboutSto l0%..of, the area at which lamination was effected, and reduction of deterioration of the laminate in water atrtemperatures higher than room temperatures.

If temperature and time ranges somewhat below those.

indicated'above are employed, the stabilizatig mfollows a different pattern of action and provides a laminate which when treated with hygroscopic plasticizing, agents of the character referred toin my prior Patent No. 2,54 6,705 havea greaterv stretchability. inthe plane of thelam nate, being capable of being stretchedfrom 2 5,.to 50%-, and with the superior clothlike and draping qualities. For example, heat treatment at;a temperature of from 360 to 375 F. at from about40 to 60 seconds; has provided a product satisfactoryfor some purposes.

After full heat treatmentfor stabilizingthelaminated material, the exterior webs or layers are; relatively inelastic and the interior web orlayer is also relatively inelastic. The bonding of theexterior webs to the stabilized interior web, particularly where the relaxing and After the heatttreatment, softening agents-may heap,

plied to the laminate. In my prior Patent.No..2',546,7 05, various hygroscopic softening agentsusuch as glycerme, ethylene glycol, and diethylene glycol, aremenhoned.

While these, are satisfactory for many'purposes, it has.

been observed 'that over long'pe'riod's of time and especially under very low relative humiditythe'seagentstend to tion is Percent Calcium chloride Glycerine in water solution 3 Another preferred formulation is Percent Calcium chloride 5 Propylene glycol in water solution 3 to 4 The use of calcium chloride tends to hold moisture as well as the glycerine or the glycols in the laminated sheet, so that a prolonged condition of softness and pliability is maintained, but additionally provides an increased flame resistant material.

The paper after treatment with such softening agent is then air dried in any desired manner, such as by the use of blowers, fans or the like.

I claim:

1. The method of making laminated sheet material having an uninterrupted interior layer of polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces of said interior layer which comprises, prior to the application of the exterior layers to the interior layer, increasing the area of the polyvinyl alcohol film by first moistening the film and then stretching the film in a plurality of directions in a water vapor saturated atmosphere.

2. The method'of making laminated sheet material having an uninterrupted interior layer of polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces of said interior layer which comprises, prior to the application of the exterior layers to the interior layer, increasing the area of the polyvinyl alcohol film by first moistening the sheet and then stretching the film in a plurality of directions in a water vapor saturated atmosphere at a temperature in the range of from about 65 to 75 F.

3. The method of making laminated sheet material having an uninterrupted interior layer of polyvinyl alcohol film and exterior layers of-thin sheet material in direct engagement with the faces of the interior layer which comprises, prior to the application of the exterior layers to the interior layer, increasing the area of the polyvinyl alcohol film by stretching the film in a plurality of directions and in excess of that desired, permitting a contraction of the area of the stretched film, and applying the exterior layers to the faces of the so contracted film.

4. The method of making laminated sheet material having an uninterrupted interior layer of polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces of the interior layer which comprises, prior to the application of the exterior layers to the interior layer, increasing the area of the polyvinyl alcohol film by stretching the film in a plurality of directions in excess of that desired, permitting a contraction of the area of the stretched film of the order of about 5 to of the largest area, and applying the exterior layers to the faces of the contracted film.

5. The method of making laminated sheet material I 6 the original area and in excess of that desired, permitting a contraction of the area of the stretched film of the order of about 5 to 10% of the largest area, and applying the exterior layers to the faces of the so contracted film.

6. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces thereof which comprises, prior to the stretching of the film, passing the film through a water saturated atmosphere, then stretching the film in a plurality of directions, and applying directly to the faces of the stretched sheet with aqueous moistening exterior webs of thin sheet material.

7. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces thereof which comprises, prior to the stretching of the film, passing the film through a water saturated atmosphere at a temperature of the order of 75 to F., then stretching the film in a plurality of directions to a plurality of times its original dimensions and applying directly to the faces of the stretched sheet with aqueous moistening exterior webs of thin sheet material.

8. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film which has been stretched in a plurality of directions to a plurality of times its original dimensions, with aqueous moistening, exterior layers of thin sheet material, and stabilizing the thus laminated material against shrinkage and delamination by exposing the laminated material to heat at a temperature below that at which charring of the exterior layers or injury to the inner layers can occur, and in the time range from about seconds to about one quarter second and at temperatures between about 360 and about 675 F.

9. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film which has been stretched in a plurality of directions to a plurality of times its original dimensions, with aqueous moistening, exterior layers of thin sheet material, and stabilizing the thus laminated material against shrinkage and delamination by exposing the laminated material to heat between metal plates to a temperature below that at which charring of the exterior layers or injury to the inner layers can occur, and in the time range from about one quarter second to about one second and at temperatures between about 440 and about 460 F.

10. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet material in direct engagement with the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film which has been stretched in a plurality of directions to a plurality of times its original dimensions, with aqueous moistening, exterior layers of thin sheet material, and stabilizing the thus laminated material against shrinkage and delamination by exposing the laminated material to heat between metal plates at a temperature below that at which charring of the exterior layers or injury to the inner layers can occur, and in the time range from about 75 seconds to about 120 seconds and at temperatures between about 360 and about 375 F.

11. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl alcohol film and exterior layers of thin sheet mate rial in direct engagement with the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film which has been stretched in a plurality of directions to a plurality of times its original dimensions, with aqueous meistening, exterior layers of thin sheet material, and stabilizing the thus laminated material against shrinkage and delamina'tion by exposing the lamina'ted material to heat from infra red heating elements at a temperature below that at which'charring of the exterior layers or injury to the inner layers can occur, and in the time range from about two seconds to about three seconds and at temperatures between about 625 and about 675 F.

12: The method of making laminated sheet material having an uninterrupted interior layer ofstretched polyvinyl alcohol film and exterior layers, of thin sheet material in direct engagement with the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film whichihas' been stretchedtin a plurality of directions to a plurality of times its original dimensions, with aqueousmoistening, exterior layers of thin sheet material, and stabilizing :the thus laminated material against shrinkage and delamination by exposing the larninated material to. heat and light pressure at a temperature below that at which charr'ing of the-exterior layers or injury to the inner layers can occur, tand in the time range from about one half second to about one and one half secon'ds and at temperatures between about 450 and about 500 F.

13. The method of making laminated sheet material having an uninterrupted interior layer of stretched polyvinyl film and exterior layers of thin sheet material in direct engagement With the faces thereof which comprises applying directly to the faces of a polyvinyl alcohol film which has been stretched in a plurality of directions to a plurality of times its original dimensions, with aqueous moistening, exterior layers of thin sheet material, and stabilizing the thus laminated material against shrinkage and delamination by exposing the laminated material to heat at a temperature below that at which charring of the exterior layers or injury to the inner layers can occur, and in the time range from about forty seconds to about sixty seconds and at temperatures between about 360 and 375 F.

14. The method of making laminated sheet material having an uninterrupted interior layer of polyvinyl alcohol film and exterior layers ofthin sheet material in direct engagement with the faces of the interior layer which 8 comprises, prior to the application of the exterior layers to the interior layer, increasing" the area'jofla sheet of polyvinyl alcohol film by stretching the sheet in a pillrality of directions to' an area of the order ofiat'least ten times the original area and in excess ofthat desired, permitting a contraction of the area of the stretched film of the order of about 5 to 10% of the largest area, applying the exterior layers to the faces of'the so contracted film, drying the laminated material, and exposingthe laminated material to heat at a temperature below that" at which charrin'g of the exterior layers or injury tothe inner layers can occur.

15. The method of making laminated sheet material having an uninterrupted interior layer of stretched ,poly.

vinyl alcohol film and exterior layers of thin sheet material in direct engagement with the facesthereofuwhich, comprises applying directly to the faces of-apolyvinylpal cohol film which has been stretched in a plurality of directions to a plurality of times itsoriginaldimensions,

with aqueous moistening, exterior layers of thin sheet'material, and applying to the exterior webs an aqueous solution containing propylene glycol, 3 t0 4%, and calcium chloride, 5%.

16. The method of making laminated sheet material having an uninterrupted interior layer of stretched-poly vinyl alcohol film and exterior'layers of thin sheetma-' terial in direct engagement with the faces thereofwhich comprises applying directly to the faces of a polyvinyl alcohol film which hasbeen stretched in'a' plurality ofdi rections to a plurality of 'times'its original dimensions,

with aqueous moistening, exterior layers'of thi'nisheet material, and then applying to'the exterior Webs an aque= ous solution containing'2 to 6% of a n'on-volatile' hygroscopic material, and 1 to 5% of a material from the group consisting of glycerine, ethylene glycol; diethylene glycol,

and propylene glycol.

References Cited in'the'file of this patent UNITED STATES, PATENTS 

1. THE METHOD OF MAKING LAMINATED SHEET MATERIAL HAVING AN UNINTERRUPTED INTERIOR LAYER OF POLYVINYL ALCOHOL FILM AND EXTERIOR LAYERS OF THIN SHEET MATERIAL IN DIRECT ENGAGEMENT WITH THE FACES OF SAID INTERIOR LAYER WHICH COMPRISES, PRIOR TO THE APPLICATION OF THE EXTERIOR LAYERS TO THE INTERIOR LAYER, INCREASING THE AREA OF THE POLYVINYL ALCOHOL FILM BY FIRST MOISTENING THE FILM AND THEN STRETCHING THE FILM IN A PLURALITY OF DIRECTIONS IN A WATER VAPOR SATURATED ATMOSPHERE. 